Calcium aluminates are a range of materials obtained by heating

calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "'' lime''" connotes calcium-containing inorganic ...

and aluminium oxide together at high temperatures. They are encountered in the manufacture of

refractories In materials science, a refractory material or refractory is a material that is resistant to Thermal decomposition, decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycr ...

and

cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixe ...

s. The stable phases shown in the

phase diagram A phase diagram in physical chemistry, engineering, mineralogy, and materials science is a type of chart used to show conditions (pressure, temperature, volume, etc.) at which thermodynamically distinct phases (such as solid, liquid or gaseous ...

(formed at

atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, ...

under an atmosphere of normal humidity) are: * Tricalcium aluminate, 3CaO·Al₂O₃ (C3A) * Dodecacalcium hepta-aluminate, 12CaO·7Al₂O₃ (C12A7) (once known as mayenite) * Monocalcium aluminate, CaO·Al₂O₃ (CA) (occurring in nature as krotite and dmitryivanovite - two polymorphs) * Monocalcium dialuminate, CaO·2Al₂O₃ (CA2) (occurring in nature as grossite ) * Monocalcium hexa-aluminate, CaO·6Al₂O₃ (CA6) (occurring in nature as hibonite, a representative of magnetoplumbite group) In addition, other phases include: * Dicalcium aluminate, 2CaO·Al₂O₃ (C2A), which exists only at pressures above 2500 MPa. The crystal is

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with ...

, with density 3480 kg·m⁻³. The natural dicalcium aluminate, brownmillerite, may form at normal pressure but elevated temperature in pyrometamorphic zones, e.g., in burning coal-mining heaps. * Pentacalcium trialuminate, 5CaO·3Al₂O₃ (C5A3), forms only under an

anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achi ...

and oxygen free atmosphere. The crystal is orthorhombic, with a density of 3067 kg·m⁻³. It reacts rapidly with water. * Tetracalcium trialuminate, 4CaO·3Al₂O₃ (C4A3), is a

metastable In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball i ...

phase formed by dehydrating 4CaO·3Al₂O₃·3H₂O (C4A3H3).

References

{{DEFAULTSORT:Calcium Aluminates Aluminates Calcium compounds Cement Ceramic materials Refractory materials

See also

References